Normally body weight and body fat in adult animals do not vary for long periods of time, despite changes in diet, activity or climatic conditions. Understanding the physiological process or processes that change the set points or "preferred" levels of body fat and cause obesity may make it possible to prevent obesity or reduce it to normal. Research work on this problem shows that the set points in body weight and body fat may be manipulated. Two examples are: 1) surgical castration in White Leghorn cockerels, normally lean, eliminates testosterone and shifts the set point in the adipose tissues and causes obesity. Injection of testosterone restores the lean body condition of the bird. 2) Electrolytic lesions in the median eminence of the hypothalamus of White Leghorn cockerels caused obesity and functional castration. Injection of testosterone or homogenized chicken pituitaries sharply decreased the level of body fat, but the cockerels remained obese. These examples show that testosterone or hormones of the pituitary are involved in setting the level of fat in the depots. In this research the role of the pituitary hormones and the hormones of the pituitary target glands, such as testosterone, estrogens, thyroxine or glucocorticoids, alone or in various combinations as they affect obesity and accompanying abnormalities, such as enlarged fatty livers, plasma triglycerides and cholesterol, will be investigated. Other hormones, such as glucagon and insulin, will also be studied. Such work may enhance the effectiveness of treatment of obesity and accompanying abnormalities.